Electrophotography is widely used not only in the field of copying machines but also for various kinds of printers in recent years because of its instantaneity and high quality of produced image. For the photosensitive member, which constitutes a core of the electrophotography, photoconductive materials such as selenium, arsenic-selenium alloy, cadmium sulfide, zinc oxide, etc. conventionally have been used. Recently, organic photoconductive materials have now been developed because of their advantage that they can be produced easily without causing environmental pollution and also can be easily formed into films.
Of the organic photosensitive members, the so-called laminated photosensitive member, which comprises a charge generation layer and a charge transport layer, have a potential of becoming a mainstream of the photosensitive member, because highly sensitive photosensitive members can be obtained by combining an effective charge-generation material and an effective charge transport material, photosensitive members having high physiological safety can be produced by selecting materials from a wide range of materials, the productivity in coating is high and they can be produced rather economically. Therefore, the development thereof is very actively being conducted today.
The photosensitive member for electrophotography is generally manufactured by providing a photosensitive layer on a substrate such as aluminum. The conditions of the substrate surface considerably influences the produced image in the practical use of the electrophotographic process. For instance, stain, foreign materials and flaws existing on the surface remarkably influence electric characteristic of the photosensitive layer and cause defects in the produced image. In order to remove such surface defects, secondary processing such as machining , technique of mirror polishing, etc. as well as precise scouring, etc. are employed. However, these processings increase the manufacturing cost.
Also as a technique for obtaining a uniform and clean substrate surface, it is known to provide a primer layer between a substrate and a photosensitive layer. Examples of the primer layer are inorganic layers such as anodized aluminum oxide film, layer of aluminum oxide, aluminum hydroxide, etc. and organic layers such as those of poly(vinyl alcohol), caseine, polyvinylpyrrolidone, poly(acrylic acid), celluloses, gelatin, starch, polyurethane, polyimides, polyamides, etc.
The primary requirement for the primer layer is that it has no adverse influence on the electrophotographic characteristics. For that purpose, the primer materials must have low electric resistance and do not undergo remarkable change in electric resistance by environmental change.
Secondly, the primer layer must be free from injection of charge carriers into the photosensitive layer. The primer layer having carrier injection property decreases the charge acceptance of the photosensitive layer, which eventually reduces the contrast in the produced image or causes fogging.
Thirdly, the primer layer must be able to be formed as thickly as possible within the range in which the electric properties of the photosensitive layer are not impaired, since it must cover various defects of the substrate surface. Further, when the primer layer is formed by application of a liquid coating composition, the coating composition must be stable.
Although various primer layers are disclosed in Japanese Laid-Open Patent Publications Nos. 48-47344, 51-114132, 58-95351, etc., those are not entirely satisfactory to the above-mentioned requirements.
We have extensively studied properties of primer materials which may satisfy the above requirements and have found that primer layers which contain a specific copolymerized polyamide are markedly effective for the above described purpose and can be formed with high productivity, and thus completed this invention.